Abstract: Trypanosoma brucei, a protozoan that causes African sleeping sickness, has a single flagellum whose function is important for motility, cell growth and pathogenesis. Eukaryotic flagellar structure is well characterized, but proteins that regulate flagellar movement are largely unknown. Flagellar motility directs swimming in some cell types but can also be critical for proper development or function of tissue such as mammalian kidney, eye and brain. T. brucei is amenable for these studies because of its tractability to molecular, genetic and biochemical techniques, but furthermore several unique aspects of the trypanosome flagellum make it important to characterize specifically. Our overall goal is to identify proteins that regulate flagellar beating, in particular we are studying the roles of components of the inner arm dynein complex of the flagellar axoneme. We have shown that IC138, an intermediate chain of dynein f, is required for flagellar movement in T. brucei: RNAi knockdown of IC138 results in immotility and growth defects. Studies of IC138 in Chlamydomonas show that it undergoes phosphorylation and is thought to inhibit microtubule sliding. Our hypothesis is that IC138 regulates flagellar motility in T. brucei. AIM 1 is to define IC138 function specifically by characterizing IC138 knockdowns in terms of changes in flagellar movement, AIM 2 is to discover functional roles of particular domains by designing site- specific mutations in IC138, and analyzing the phenotypes of mutants, and AIM 3 is to identify candidate protein partners that facilitate IC138 function using biochemical approaches. Because T. brucei flagellar beating patterns show waveforms that are distinct from those of other flagellated eukaryotes, these studies extend our understanding of the regulation of flagellar motility generally, and thus complement and extend studies of IC138 in other organisms. This is a robust model system that we have used successfully for undergraduate summer and senior honors projects. Students develop fundamental science skills, learn to work independently and give presentations on research and on relevant literature. The research has significance both for biology of these pathogens and for the understanding of human diseases caused by flagellar defects.